1. Technical Field
The present invention relates to a color controlling method in a digital color display system, particularly to a method and an apparatus for tint control of a display color in a digital color display system.
2. Prior Art
In the case of a color display system such as an LCD (Liquid Crystal Display) or CRT, it is ideal to make colors which can be expressed by the system approach natural colors as close to as possible (display color fidelity). Moreover, it is also eagerly desired that the system automatically controls or a user manually controls a color in accordance with the environment in which the system is set such as illumination so that an optimum color corresponding to each environment can be displayed (color calibration) or the same color can be outputted independently of a color display system for outputting colors (device transfer characteristics). These operations are generally referred to as color management which is an important field in which various studies and researches are performed as an item indispensable for a color display system (particularly, high-performance model) from the next generation downward. For example, white point adjustment is an item whose significance has been recognized so far and which has been actually realized in a color monitor or the like.
Color control such as control of tints between red, yellow, and green (tint control: from reddish yellow to greenish yellow) or control of color depth (from complete monochrome to deepest color), which is frequently performed for a color TV can be said to be an indispensable color control item for TV and the like though the color control is not so important as control of a white point for a color monitor of an office user. Tint control is a reminder of the period in which the fluctuation of display color characteristics was large among television receivers when a color TV first appeared. However, even at present, an audience particularly sensitive to the color of a person""s face positively uses the tint control. Therefore, color TVs up to now are respectively provided with a tint control function independently of whether a display unit uses a CRT or an LCD.
Though details of the theory of the tint control for an NTSC-system color TV are left to books related to color TVs, the outline of the theory is described below. In the case of the NTSC system, three primary color signals of R, G, and B are transformed to a luminance signal Y and color signals I and Q and then transmitted. Signals. I and Q are amplitude-modulated (AM) by two color subcarriers having the same frequency and having phases shifted from each other by 90xc2x0 respectively. A carrier color signal which is generated by combining the above modulated signals is multiplexed to the luminance signal Y to finally obtain a composite color signal. (so-called a video signal). It is publicly known to further frequency-modulate (FM) the composite color signal and superimpose it on a radio wave in the case of ground-wave analog broadcast. FIG. 11 shows a waveform of the composite color signal when displaying a color-bar test pattern. FIG. 12 shows the phase and amplitude of the carrier color signal of each color of the color bar test pattern in the form of vectors in the above case.
In a color TV, a composite color signal is divided into a luminance signal Y and a carrier color signal by a Y/C separation circuit. Moreover, the carrier color signal is demodulated by two reference color subcarriers having phases 90xc2x0 shifted from each other generated in accordance with a color burst signal multiplexed on the composite color signal and thereby, R-Y component (value obtained by subtracting luminance Y from red component) and B-Y component (value obtained by subtracting luminance Y from blue component) are obtained. Furthermore, G-Y, component (obtained by subtracting luminance Y from green component) is generated from R-Y and B-Y by a matrix circuit and added to the luminance signal Y separated by the Y/C separation circuit respectively and thus, R, G, and B signals are obtained.
In this case, by delaying or advancing the relative phases of the reference color subcarriers to the phase of the color burst signal from the normal phase, obtained R-Y and B-Y have values different from normal values. FIG. 13(a) shows a case of slightly delaying the relative phase (xe2x88x92xcfx86), which, as shown in FIG. 13(b), almost corresponds to a case of obtaining a color shown by a vector as if rotated counterclockwise by xcfx86 in the vector space in FIG. 12 (Although there is a slight error of the signal amplitude (color purity) in case of slightly delaying the relative phases by xcfx86, it can be ignored when xcfx86 is very small). FIG. 13(c) shows a case of slightly advancing the relative phase (+xcfx86), which, as shown in FIG. 13(d), almost corresponds to a case of obtaining a color shown by a vector as if rotated clockwise by xcfx86 in the vector space in FIG. 12.
To shift the relative phases, a method of applying phase correction to a circuit for generating reference color subcarriers from a color burst signal in accordance with L, R, and C has been generally used so far for an analog TV. For a digital-signal-processing TV, however, a method according to the matrix operation of R-Y and B-Y signals is generally used as shown in FIG. 14.
The above-described methods cannot be applied to color monitors having a video I/F using digital or analog R, G, and B inputs but having no Y/C separation system. Among these monitors, even if they respectively use an analog video I/F, a monitor that processes video data by transforming the data to digital data is mainly used at present independently of a CRT or LCD monitor. Particularly, LCD monitors having a digital video interface using a low-voltage-differential-transfer-type digital data transmission system such as LVDS or TMDS (PanelLink) are being spread. In these monitors, every video signal is processed as digital data until the signal is inputted to the source driver (X driver) of an LCD module after it is outputted from a graphics controller. Moreover, in the case of a notebook-type PC, because a system section (including a graphics controller) and a display section (LCD module) are integrated, digital data is used until the data is inputted to the source driver of an LCD module from a graphics controller.
To perform the above tint control in this digital-type color display system, it is necessary to transform R, G, and B digital data values. For a color tone conversion system according to transform of digital color data, the official gazettes of Published Unexamined Patent Application Nos. 7-99586 and 7-99587 respectively disclose a system of-obtaining a transformed value by preparing expected transformed values to the combination of many sample input color values in the form of a table (referred to as Look Up Table: LUT) and interpolating values obtained from the loop-up table for colors other than sample input colors in accordance with the information in the table. However, it is necessary for these transform systems to have a Look Up Table in a ROM and the interpolation circuit is generally complex. As a result, the circuit requires a very large size and it is necessary to have a Look Up Table for each type of transform parameter. Moreover, because the tint control function has a strong aspect that it is preferable to have the function, it is not desirable that-many circuits are required for the function.
The present invention is made to solve the above problems and its object is to provide a method and an apparatus for controlling a tint in a digital color display system capable of efficiently performing tint control of colors displayed on the digital color display system by a simple circuit.
The present invention relates to a method and an apparatus for making it possible to control the tint of a color displayed by a display system by transforming original digital color data inputted from a host machine in accordance with several set values supplied from the outside of the system in a digital color display system. That is, the present invention relates to a method for controlling a tint in a digital color display system, wherein a digital video interface for, inputting a digital video signal outputted from a host machine is used and thereby, color transform is applied to the digital video signal inputted through the digital video interface without using a Look Up Table and moreover, three primary colors constituting the display colors are referred to as R, G, and B for convenience"" sake and each color is expressed by n-bit (n: integer equal to or larger than 1) digital data. Moreover, the present invention is characterized by using a method for controlling a tint in a digital color display system, comprising the steps of:
(1) when the maximum and the minimum values among R, G, B are the maximum gray scale value (=L=2nxe2x88x921) and the minimum gray scale value (=0) respectively, a step of transforming the input color into a color of a different tint having the maximum value among R, G, B equal to the maximum gray scale value (=L=2nxe2x88x921) and the minimum value among R, G, B equal to the minimum gray scale value (=0) , based on a user defined maximum transformation value (=Atm) and a transformation direction (either from (R, G, B)=(L, 0, 0) via (R, G, B)=(0, L, 0) to (R, G, B)=(0, 0, L) or (R, G, B)=(0, 0, L) via (R, G, B)=(0, L, 0) to (R, G, B)=(L, 0, 0));
(2) when the maximum and the minimum values among R, G, B are Dmax and Dmin respectively (0 less than Dmin less than Dmax less than L=2nxe2x88x921), a step of transforming the input color into a color of a different tint having the maximum value among R, G, B equal to Dmax and the minimum value among R, G, B equal to Dmin, based on a smaller transformation value At computed from the Atm and the transformation direction same as the case of the Atm; and
(3) when all values of R, G, B are equal, a step of not transforming the input color in accordance with any input set value.
Moreover, an apparatus of the present invention for controlling a tint in a digital color display system is an apparatus for executing a tint control method in the above digital color display system, constituted so that an output value after transformed is outputted in a pipeline manner to an input value before transformed as a whole, by using the transform of a line segment to integers using the core calculation function Z=f(X, Y) constituted so that Z is outputted for inputs X and Y in a pipeline manner by hardware as the basis of transform.
Moreover, the present invention shows a transform formula and a circuit configuration for constituting a system for transforming successively-inputted digital color data synchronously with a pixel clock through a certain number of clock cycles and outputting the data in a pipeline manner by a relatively simple circuit by using a circuit block as the basis of transform, which realizes the core calculation function Z=f(X, Y), whose core is an algorithm of approximating a line segment in an orthogonal two-dimensional coordinate system with efficient calculation to points having integral coordinates.